A colleague from Australia – wanting the smoothest possible surface for his kiln-fired painted stained glass – wrote and asked us how we prepared our trays …
We ourselves use whiting (calcium carbonate).
To stop hot glass sticking to the surface of a kiln, whiting is a far simpler solution than, for example, kiln spray, fibre board or kiln paper. And, generally, for a craft which has been going as long as stained glass, the simplest and least technical solutions are best.
Now the important thing is to make sure the whiting is really compressed.
You must squeeze out all hidden pockets of air, and the surface must be smooth.
Now why on earth go to all this trouble?
This is how to stop your glass from sticking when it heats, and how to leave its underneath as smooth as silk.
So turn on your speakers and take a look at this video on your right: you’ll see what we do. It’s me (David) doing all the hard work, while my inestimable colleague (Stephen) does the voice-over …
As always, your comments and questions are welcome and will be helpful to all the other glass painters who visit here.
Postscript in answer to Bill Wrobel
Our trays are made from mild steel. They are each made from four L-shaped bars which are duly welded together to make a tray with a large hole in the middle. To cover this hole, we insert a neatly fitting piece of fibreboard. The whiting is sprinkled and compressed on top.
Thank you, Bill!
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Thanks a lot for this, it’s very interesting and informative.
I have had problems with certain kiln papers reacting badly with painted glass when fired painted side down. Have you noticed any adverse reactions at all with the whiting?
Also, I am curious as to the provenance of your mild steel trays. Do you have them specially made?
Seasons greetings to you both!
Hi Jackie,
Thanks for your comment and questions. Like you, we have had problems with kiln paper – probably because it itself is a source of potentially contaminating fumes.
As for adverse reactions arising from whiting, these have only occurred when, through haste, we neglected to ensure the previously used whiting was as clean as it should have been. Say you’ve painted both sides of the glass and want to fire them in a single firing. Then, necessarily, one of the painted surfaces will be in contact with the whiting. And some paint powder will probably be released into the whiting before the firing. This must be removed before the next firing.
Similarly, it’s sometimes possible for a single firing to combine tracing and shading on the top surface of the glass with silver stain on the underneath. Once again, some silver stain will probably be released onto the whiting. Once again, this must be removed before the next firing.
A blacksmith made our trays. But you just need to find a material that won’t warp in the heat of the kiln.
Every best wish to you, and maybe we will see you again in 2010.
Stephen
What a splendid idea! So, an inspection of the whiting after a firing is all that is needed? That is, you want to bring it back to the stage it was before firing? Slightly grey fired whiting is OK to use again?
How thick are the trays and how high is the lip on the trays you use?
I am going to have a round one made.
Wonderful video, thank you for sharing it. Your wealth of information and your eagerness to share it is delightful.
Happy and safe New years to you and yours!
Shereen
Hi Shereen,
Thanks so much for your enthusiasm and support!
You ask about re-using dirty whiting. You specifically mention whiting that is slightly grey. And, indeed, this is the colour that whiting will become by virtue of the fumes and dust that is “fired off” in the normal course of firing your painted stained glass. Now this is surface grime. So, typically, it’s fine to continue using this slightly discoloured whiting. But everyone must use their own discretion here. If you’ve spent days painting a piece of clear white glass (as opposed to, for example, deep blue), then it’s no doubt better to use new whiting in order to avoid the slight risk of discolouring your delicate painting.
You also ask about the trays themselves. We use trays made from 1/8 inch gauge mild steel which are ½ inch deep. Ours were made by a local blacksmith. But the main thing is that you need to be confident that the trays don’t warp under the kind of heat to which you will subject them.
I hope this helps. Please always ask more questions as needed because it’s also useful to other people and allows us to see the other things we need to mention.
Thanks for your good wishes, Shereen! We too wish you every happiness and success to you in 2010.
Stephen
I use a large kiln because of the size of the church windows I create. I have been using Plaster of Paris as a cushion on the kiln floor. It seems to work well although it is messy when retrieving fire pieces. The powder will cling to the glass. But it doesn’t stick. – It just has to be brushed off. When laying down a layer of this product I smooth it with a squeegee. Should I press it also?
Hello Jack,
Thanks for your comment. It’s always helpful to us and others to know what works for different people. You ask whether you should also press the Plaster of Paris. Truthfully, now, what can I say? Myself, I’d certainly want to know that all pockets of air had been removed from any powder – whether whiting or Plaster of Paris, or anything else – that I’d used in order to prevent the heated glass from sticking to the kiln.
Maybe you’re using such a fine layer that there’s no air to expel.
Can you say?
Here’s the point: we can tell you and others what works for us – this doesn’t mean it’s the only thing which works. Therefore it’s wonderful that you and others also join in and say what works for you. Thanks so much!
All the best,
Stephen
P.S. Thank you also for sending us an image of the kind of glass painting that you do. It’s always so helful for us to know something of the direction that you are heading for. We’re therefore always glad when you and others send us images of their work. Thank you!
Thank you so much for the video. That technology is perfect for this type of communication.
Now it looks like there is/are a sheet or two of 6mm fibreboard at the bottom of your tray before you add whiting in the video.
Is this correct – or is it just more whiting that I am seeing?
And again thank you for sharing this tip.
Hi Bill,
Thanks for your comment. You are absolutely right in your observation. We should have made this clear in the main body of the post. We will now add a comment there to that effect.
The tray itself is made from 4 separate pieces of mild steel whose profile is L-shaped. These are then duly welded together to form a tray with a large hole in the middle.
To plug the hole, we insert a piece of fibreboard which is used pretty much forever because it doesn’t suffer any wear-and-tear.
Thanks so much, Bill, for pointing out the need for clarification here!
All the best,
Stephen
Hello David and Stephen!
This is rather ’spooky’! I find I have a few days to spare and thought I would look at achieving a better result when firing using whiting. Just then your email arrived. In a way you have given me some more ‘play’ time now because I shall hurry on over to a super local blacksmith that I know and talk about making a tray (or two?).
A question: does one have to dry off the whiting in the kiln (just in a pile on the bat) and then sieve it before using it as you describe?
If this is necessary, then at what temperature and for how long, please? (I have a feeling I may be thinking of plaster of Paris – some years ago before I came and did a course with you two, the guy who taught us said we had to bake out the whiting before using it to work with).
Clarification would be most gratefully received. And let me tell you how very much I enjoy your frequent messages.
I wish you a very happy new year!
All the very best,
Shelagh
Hi Shelagh,
A very Happy New Year to you as well! And thanks for your comment and question.
Now we don’t dry out the whiting. We just use it straightaway.
All the best,
Stephen
P.S. As with all these things, different situations can give rise to different results. So the best thing is always to march forward armed with good advice and always be prepared to make your own observations and conclusions.
Stephen and David,
Thanks ever so much for your continued efforts to promote the excellence of painting on glass.
I am curious about the gage of the metal you use for the trays shown in the video. Obviously, it isn’t necessary to use 1/4″ steel, but what do you use or recommend?
Also, did you get the recent referral I sent to you via Allexperts.com. (I noticed some time ago that you all were co-contributors to the site.)
Again, thanks you all for your generosity.
Carl Trimble
Trimble Studios
Dallas, Texas
Hello Carl,
Thanks for your kind comment. It is indeed our good fortune to have this contact with you. Just imagine that, a mere 10 years ago, we would all of us have been pretty much confined to our studios. And now we can talk like this and discuss ideas together!
You also asked a question: our own trays are made from 1/8 inch gauge mild steel which are ½ inch deep. As noted earlier, each side of the tray has an L-shaped profile.
All the best,
Stephen
P.S. I can’t be certain we did get your referral from AllExperts. But I’ve checked our inbox, and everything is answered and up-to-date.
P.P.S. So that other folks know, this is Carl’s profile on AllExperts.